Operational Performance and Status of the ATLAS Pixel Detector at the LHC

The ATLAS Pixel Detector is the innermost detector of the ATLAS experi- ment at the Large Hadron Collider at CERN. The detector provides hermetic coverage with three cylindrical layers and three layers of forward and backward pixel detectors. It consists of approximately 80 million pixels that are individu- ally read out via chips bump-bonded to 1744 n+-in-n silicon substrates. In this talk, results from the successful operation of the Pixel Detector at the LHC and its status after three years of operation will be presented, including moni- toring, calibration procedures, timing optimization and detector performance. The record breaking instantaneous luminosities of 7.7 · 1033 cm−2s−1 recently surpassed at the Large Hadron Collider generate a rapidly increasing particle fluence in the ATLAS Pixel Detector. As the radiation dose accumulates, the first effects of radiation damage are now observable in the silicon sensors. A regular monitoring program has been conducted and reveals an increase in the silicon leakage current, which is found to be correlated with the rising radiation dose recorded by independent sensors within the inner detector volume. In the longer-term crystal defect formation in the silicon bulk is expected to alter the effective doping concentration, producing type-inversion and ultimately an increase of the voltage required to fully deplete the sensor. The fourth pixel layer at the radius of 3.5 cm will be added during the long shutdown 2013-2014 together with the replacement of pixel services.